[PATCH RESEND] lib/x86_64/setjmp: Use 32-bit zero idiom for shorter encoding

[PATCH RESEND] lib/x86_64/setjmp: Use 32-bit zero idiom for shorter encoding

[George Hu]

Switch from `xorq %rax, %rax` to `xorl %eax, %eax`. In 64-bit mode,
zeroing EAX implicitly clears RAX, and the 32-bit form encodes one
byte smaller while keeping identical semantics.

Signed-off-by: George Hu <integral@archlinux.org>
---
 grub-core/lib/x86_64/setjmp.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/grub-core/lib/x86_64/setjmp.S b/grub-core/lib/x86_64/setjmp.S
index 6b151bc4d..4c6c81249 100644
--- a/grub-core/lib/x86_64/setjmp.S
+++ b/grub-core/lib/x86_64/setjmp.S
@@ -36,7 +36,7 @@ GRUB_MOD_LICENSE "GPLv3+"
  */
 FUNCTION(grub_setjmp)
 	pop	%rsi		/* Return address, and adjust the stack */
-	xorq	%rax, %rax
+	xorl	%eax, %eax
 	movq	%rbx, 0(%rdi)	/* RBX */
 	movq	%rsp, 8(%rdi)   /* RSP */
 	push	%rsi
-- 
2.52.0


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Re: [PATCH RESEND] lib/x86_64/setjmp: Use 32-bit zero idiom for shorter encoding

[Daniel Kiper]

On Wed, Nov 26, 2025 at 04:45:46PM +0800, George Hu wrote:
> Switch from `xorq %rax, %rax` to `xorl %eax, %eax`. In 64-bit mode,
> zeroing EAX implicitly clears RAX, and the 32-bit form encodes one
> byte smaller while keeping identical semantics.
>
> Signed-off-by: George Hu <integral@archlinux.org>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel

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